Unfortunately hiding a category is not a solution. Only 'normal' categories will be exported to StoreYa - no 'hidden' categories.
We always recommend setting up a separate store just for import into StoreYa but that would mean - as you currently have a 1 site plan - you have to upgrade to a multiple store plan (5 or unlimited).
Or you can upgrade to a paid Storeya subscription so you can import more products into your Facebook page. You can save 25% at StoreYa with the code: Datafeedr_Coupon